1. Field of the Invention
The present invention relates to a substrate heating apparatus including a hot plate for heating a substrate coated with a coating solution and a cooling plate for cooling the heated substrate, a coating and developing system employing the heating apparatus, and a method of heating a substrate.
2. Description of the Related Art
A known coating and developing system coats a substrate (e.g., a semiconductor wafer, or a glass substrate for a liquid crystal display) with a resist solution and develops an exposed resist, in order to form a resist pattern on the substrate. Such a coating and developing system employs a heating apparatus that is generally called “baking apparatus”. For instance, the baking apparatus heats a wafer coated with a resist solution to vaporize a solvent contained in the resist solution to dry the resist solution.
FIG. 20 shows the structure of the aforementioned heating apparatus in one example. Reference numeral 10 denotes a casing, and reference numeral 10a denotes a wafer delivery port. Reference numeral 11 denotes a base plate, and reference numeral 12 denotes a cooling plate for cooling a wafer adapted to move toward a hot plate 12a. Drive mechanisms 13 and 14 are arranged in a space below the base plate 11 to vertically move pins 13a and 14a, respectively. Vertical movement of the pins 13a by the drive mechanism 13 assists the transferring of a wafer between the cooling plate 12 and a not shown wafer conveyer that enters the casing 10 through the wafer delivery port 10a. Vertical movement of the pins 14a by the drive mechanism 14 assists the transferring of the wafer between the cooling plate 12 and the hot plate 12a. Reference numeral 15 denotes a cap-shaped top plate that moves vertically by a driving mechanism 15a. 
When the wafer W is placed on the hot plate 12a, the top plate 15, which serves as a gas flow guide and is arranged above the base plate 11, descends to contact closely to the base plate 11 via an O-ring 15b to define a sealed space around the wafer W, as shown in FIG. 21. Thereafter, a gas supply unit 17a supplies a gas into the sealed space through gas supply ports 17 circumferentially arrayed around the wafer W, while a suction unit 18a suctions a gas in the sealed space through a suction port 18 arranged at the central portion of the top plate 15. Thereby, the wafer W is heated while the gas flows from the peripheral portion towards the central portion of the wafer W, as indicated by arrows.
The aim of the provision of the cooling plate is to improve the throughput of the coating and developing system. In detail, after the wafer (i.e., substrate) is subjected to a heating process in the heating apparatus, the substrate is conveyed to a cooling apparatus that cools the substrate to a designated temperature with high temperature accuracy. As a substrate conveyer, which conveys substrates between apparatuses included in the coating and developing system, is operated according to a predetermined conveying schedule, the substrate having been heated by the hot plate of the heating apparatus must stand by in the heating apparatus for transfer to the cooling apparatus by the substrate conveyer, for a predetermined time period. If the substrate is cooled (pre-cooled) during this time period, the cooling process time in the cooling apparatus can be shortened. This may results in improvement of throughput of the coating and developing system, and may provide a possibility of reducing the total number of the cooling apparatuses included in the coating and developing system. The above is the reason for the provision of the cooling plate in the heating apparatus.
In former years, a cooling plate and thus the substrate plated on the cooling plate in the heating apparatus is cooled by a cooling liquid flowing through cooling liquid tubes arranged in or on the cooling plate. Such a cooling structure is associated with a risk of leakage of the cooling liquid from the cooling liquid tubes. In addition, as the cooling liquid tubes meandering through the interior of the heating apparatus bend and stretch, the freedom of layout design of the driving mechanism for moving the cooling plate is greatly limited. Moreover, the structure of the cooling plate and the relevant component parts is complicated, the number of the component parts is large, and the maintenance of the cooling mechanism is troublesome.
In order to solve the above problems and to simplify the whole structure of the heating apparatus, a heating apparatus employing heat pipes instead of the aforementioned cooling liquid tubes has been recently proposed.
JP2001-203152A discloses a heating apparatus provided with a cooling mechanism including a cooling plate and heat pipes embedded in the cooling plate. The cooling plate has a first end portion located in a cooling chamber on which a substrate to be cooled is placed, and a second end portion located outside the cooling chamber and having plural air-cooled fins on the upper and lower surfaces of the second end portion. The heat pipes extend from the first end portion to the second end portion of the cooling plate. The air-cooled fins are naturally cooled, or are cooled by an optional fan arranged above the second end portion of the cooling plate to generate air flow flowing toward the air-cooled fins. The substrate placed on the first end portion of the cooling plate is effectively cooled through heat transfer from the first end portion to the second end portion of the cooling plate via the heat pipes.
The cooling mechanism of JP2001-203152A has the following problems. The fan must be arranged near the air-cooled fins in order to achieve a high cooling efficiency. This limits the freedom of layout design of the heating apparatus. In addition, in order to achieve a higher cooling efficiency, the size of the fan and/or the number of fans must be increased, and thus a larger space is required to arrange the fan or fans, resulting in increase of the whole size of the heating apparatus. This problem becomes more significant if the substrate size is larger. Moreover, the air flow generated by the fan may possibly raise particles, contaminating the substrate and the internal atmosphere in the heating apparatus.
JP2001-230172A discloses a heating apparatus provided with a cooling mechanism including a cooling plate and a heat pipes embedded in the cooling plate. The cooling plate has a first end portion on which a substrate to be cooled is placed, and a second end portion. The heat pipes extend from the first end portion to the second end portion of the cooling plate. The cooling plate internally provided, in the second end portion thereof, with a heat exchanging device to which the proximal ends of the heat pipes are thermally connected. A cooling medium such as water is supplied to the heat exchanging device through a cooling medium supplying and discharging pipes drawn out of the cooling plate.
The cooling mechanism JP2001-230172A still has problems of the leakage of the cooling medium and of the complicated arrangement of cooling-medium pipes and the component parts involving the supply of the cooling medium, which problems are associated with the heating apparatus in the former years described above.